In the e-commerce world, the follow-up of prices in detail web pages is of great interest for things like buying a product when it falls below some threshold. For doing this task, instead of bookmarking the pages and revisiting them, in this paper we propose a novel web data extraction system, called Wextractor. It consists of an extraction method and a web app for listing the retrieved prices. As for the final user, the main feature of Wextractor is usability because (s)he only has to signal the pages of interest and our system automatically extracts the price from the page.